1. Field of the Invention
The present invention relates, in general, to wireless communication systems and, more particularly, to the handoff of a mobile station from a first base station to a second base station in code division multiple access (CDMA) communication systems.
This is a counterpart of and claims priority to Japanese patent application Serial Number 313591/2001, filed Oct. 11, 2001, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art
Diversity transmission in a CDMA system is disclosed in “Physical channels and mapping of transport channels onto physical channels (FDD)” 3GPP (3rd Generation Partnership Project). A closed loop mode diversity transmission is disclosed which controls a transmitting carrier phase of a base station (Node B) using feedback information output from a mobile station (UE: User Equipment). Diversity is a generic name for methods of receiving a plurality of same signals under the several differential requirements and selecting the signal meeting a certain requirement or communicating condition. Diversity transmission generates a plurality of carrier waves each of which has the differential wave modulated using the same modulation signal, and transmits the generated carrier waves to a plurality of paths having individual fading.
However, the above document does not disclose a method of diversity transmission among two or more base stations, when the mobile station is in the handoff situation from one base station to another base station. The mobile station does not individually direct the selection of diversity transmission of one base station to be communicated next, when the mobile station is communicating with the other base station.